Identification of Thinopyrum distichum chromosomes responsible for its salt tolerance
A Thinopyrum distichuml 4× rye (Secale cereale) hybrid with genomes J1dJ2dRR was pollinated with diploid rye and mostly yielded F1 offspring with 21 chromosomes (two complete rye genomes and seven Thinopyrum chromosomes). Apparently, the closely related homoeologous chromosomes of the J1d and J2d genomes regularly formed bivalents during megasporogenesis, and egg cells mostly received a random, yet balanced set of seven Thinopyrum chromosomes. F1 plants were tested for salt tolerance and a set of fifteen highly salt-tolerant F1 plants were selected and maintained as clones for several years. These were C-banded and the Thinopyrum chromosomes contained in each were determined. By comparing segregation patterns it was now possible to group the Thinopyrum chromosomes into seven homoeologous pairs. For each of four homoeologous pairs, one of its members occurred at a higher than expected frequency, implying that these chromosomes are expressed under salt stress conditions. The results could be confirmed by backcrossing two of the most tolerant F1 plants to diploid rye. While the critical chromosomes can be identified through C-banding, an attempt was made to also find a RFLP marker for each. RFLP probes, diagnostic for the group 2, 3, 4 and 5 homoeologues of wheat, detected polymorphisms on the respective critical Thinopyrum chromosomes. However, the preliminary allocation of the critical chromosomes to homoeology groups needs to be confirmed using more and varied markers.